1. Field of the Invention
The present invention relates to a displacement information detection apparatus used in the field of machine tools, measuring apparatus, and the like in order to detect linear shifting and rotary shifting of an object; a detection device suitable therefor and a drive control apparatus using said displacement information detection apparatus.
2. Related Background Art
Recently, small-size, light-weight and high-performance linear encoders, rotary encoders, and so on which detect shifting of a moving object have become needed. Especially, when assembled in steppers, machine tools, various kinds of robots for manufacture, and so on, small-size, light-weight and highly precise encoders are desired.
FIG. 1 is a schematic view of the main portions of a typical encoder in the prior art. The encoder shown in the figure comprises two slit rows; a slit row provided in a main scale 64 and slit rows formed in a secondary scale 65.
In the same figure, a beam outgoing from a light-emitting element 61 is bent by a mirror 62, collimated by a lens 63 and incident on the main scale 64. The main scale 64 is a transparent material such as glass and the like or a thin metal plate, on which the slit row consisting of transmitting slit-shaped apertures of the same width and shielded portions is formed by means of etching, or the like.
The beams transmitted through the main scale 64 are incident on the secondary scale 65 in which the apertures have the same intervals as those of the apertures in the main scale 64. The beams transmitted through the apertures of the secondary scale 65 are received by a light receiving means 66.
The main scale 64 is fixed to the object to be measured (not shown), but is capable of relative motion, with respect to a detection head unit 60 indicated by dashed lines in FIG. 1, in the direction indicated by the arrow A.
Light or dark signals, due to the shutter effect by the apertures of the main scale 64 and those of the secondary scale 65, are generated on the surface of the light-receiving means 66 accompanying a motion of the main scale 64. The light receiving means 66 detects the light or dark signals, thereby measuring shifting states of the main scale 64, that is, shifting states of the object to be measured.
Though the conventional encoder shown in FIG. 1 is already small and is manufactured at a low cost, the number of components thereof is large, which limits the minituarization of the whole apparatus. Further, it is difficult to adjust the component position in assembling the encoder, which also limits the possible reduction in cost of the apparatus.